This application is based on applications Nos. H10-286152, H10-286153, H10-286154, H10-286179, H10-286181, and H10-286183 filed in Japan on Oct. 8, 1998, and Nos. H10-303659, H10-303715, H10-303726, H10-303730, and H10-303733 filed in Japan on Oct. 26, 1998, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a projector, i.e. a projection-type image display apparatus, and to a light source unit for a projector.
2. Description of the Prior Art
A projector modulates light in accordance with an image, and projects the modulated light on a screen to display the image thereon. A projector is used to present an image to a number of people at a time, and is nowadays used even as a television monitor having a comparatively large screen.
FIG. 51 shows an example of the construction of a conventional projector, in the form of a horizontal cross section including the optical axis of the projection lens thereof. The projector 114 is composed of an illumination section, a display section, and a projection section. The illumination section illuminates the display section uniformly. The display section separates the illumination light into illumination light of three colors, i.e. red (R), green (G), and blue (B), then converts the illumination light of three colors individually into optical images of the corresponding colors, and then integrates the optical images of three colors together. The projection section projects the resulting integrated optical image.
The illumination section is provided with a light source 101 composed of a metal-halide lamp, a reflector 1OZ formed as a reflecting mirror having the shape of a paraboloid of revolution so as to reflect the light emitted from the light source 101 and thereby form the light into a substantially parallel beam of light, a first lens array 103 and a second lens array 104 each having a plurality of lens cells arranged in a matrix, and a superimposing lens 105.
The first lens array 103 is so arranged as to be optically conjugate with the three liquid crystal display panels 111R, 111G, and 111B, which constitute the display section. The individual lens cells of the second lens array 104 are so arranged as to be optically conjugate with the light source 101.
The white light emitted from the light source 101 is reflected by the reflector 102 so as to enter the first lens array 103, which then separates the light into a plurality of light beams. These light beams enter the second lens array 104, and then form a plurality of light source images. That is, the individual lens cells of the second lens array 104 serve as a secondary light source. The plurality of light beams exiting from the second lens array 104 are superimposed on one another by the superimposing lens 105, and are led to the individual liquid crystal display panels 111R, 111G, and 111B of the display section.
Next, the display section will be described. The display section is provided with, in addition to the liquid crystal display panels 111R, 111G, and 111B that convert illumination light of three colors individually into optical images, field lenses 110R, 110G, and 110B provided in front of the liquid crystal display panels 111R, 111G, and 111B respectively, dichroic mirrors 106a and 106b that each transmit light of a specific wavelength range, turning mirrors 107a, 107b, and 107c, a condenser lens 108, a relay lens 109, and a cross dichroic prism 112.
The dichroic mirror 106a transmits only R-color light. The dichroic mirror 106b transmits only B-color light. The R-color light transmitted through the dichroic mirror 106a is then reflected by the turning mirror 107a so as to pass through the field lens 110R and then illuminate the liquid crystal display panel 111R. The G-color light reflected from the dichroic mirrors 106a and 106b passes through the field lens 110G and then illuminates the liquid crystal display panel 111G. The B-color light reflected from the dichroic mirror 106a and transmitted through the dichroic mirror 106b travels via the condenser lens 108, the turning mirror 107b, the relay lens 109, the turning mirror 107c, and the field lens 110B, and then illuminates the liquid crystal display panel 111B.
The distance from the light source to the liquid crystal display panel 111B is different from the distance from the light source to the liquid crystal display panel 111R or 111G. This is the reason that the condenser lens 108 and the relay lens 109 are used, which serve to make the illumination condition of the liquid crystal display panel 111B identical with that of the liquid crystal display panel 111R or 111G. The field lenses 110R, 110G, and 110B serve to achieve telecentric illumination of the liquid crystal display panels 111R, 111G, and 111B.
The cross dichroic prism 112 has a cementing surface 112a to which a dichroic coating that reflects only B-color light is applied and a cementing surface 112b to which a dichroic coating that reflects only R-color light is applied. On the liquid crystal display panels 111R, 111G, and 111B are formed optical images of the R, G, and B colors respectively. The light beams conveying these optical images enter the cross dichroic prism 112, where they are integrated together as a result of the R-color light being reflected by the cementing surface 112b and the B-color light being reflected by the cementing surface 112a. The resulting integrated light beam is then led to the projection lens 113, which constitutes the projection section. The projection lens 113 projects the light beam led thereto on a screen (not shown).
As described previously, the plurality of light beams exiting from the second lens array 104 of the illumination section are superimposed on one another when illuminating the liquid crystal display panels 111R, 111G, and 111B. This makes it possible to illuminate the liquid crystal display panels 111R, 111G, and 111B with an uniformly distributed amount of light, and thereby form a color image with uniformly distributed brightness on the screen.
A projector is expected to project a bright image efficiently. To achieve this, various projectors have conventionally been proposed that are provided with some means that serves the purpose. For example, in the conventional projector shown in FIG. 51 and described above, uniform illumination is achieved by an ingenious design of the illumination section to make it possible to use the light from the light source efficiently and thereby project a bright image.
Moreover, in recent years, developments have been made also in technologies related to lamps for use as a light source. By the use of a bright lamp, it is possible to obtain bright illumination easily. As an example of recently developed lamps, an ultra-high-pressure lamp (UHP lamp) is known. A UHP lamp offers higher efficiency than a metal-halide lamp as is used as the light source in the conventional projector described above. FIG. 52 shows a graph representing the relationship between brightness and electric power consumption for these two types of lamp.
In FIG. 52, the horizontal axis represents brightness, and the vertical axis represents electric power consumption; the dash-and-dot line 150 indicates the relationship observed in a metal-halide lamp, and the solid line 151 indicates the relationship observed in a UHP lamp. For example, to obtain brightness I1, whereas a metal-halide lamp requires electric power consumption W1, a UHP lamp requires W2, which is lower than W1. In other words, with the same electric power consumption W1, a UHP lamp offers brightness 12 higher than the brightness I1 that a metal-halide lamp offers.
That is, in comparison with a metal-halide lamp, a UHP lamp offers given brightness with less electric power consumption, and thus permits brighter display without extra electric power consumption. The higher the electric power consumption, the higher the running costs. Moreover, the higher the electric power consumption, the shorter the life of the lamp, and therefore, quite disadvantageously, it is difficult to maintain stably bright display of images for a satisfactorily long period.
In general, a projector is designed to adopt a lamp that is considered to be the best available on the whole at the time of design. Today, projectors that adopt a UHP lamp are already commercially available. It is therefore very likely that future developments will bring about a new-technology lamp that offers higher efficiency, i.e. a superior brightness/electric power consumption relationship, as indicated by the broken line 152 in FIG. 52.
However, conventional projectors allow use of only one specified type of lamp, and light emission is controlled on the basis of the ratings set for that lamp. Thus, even if new developments are made in lamp technologies, it is not possible to use a lamp of the latest type in place of the specified type. In order to use a lamp of the latest type, quite uneconomically, the projector proper needs to be replaced with a new one that is compatible with a lamp of the latest type.
Every lamp has a life, and thus cannot be lit forever. Accordingly, the user of a lamp needs to replace the lamp when necessary. In so doing, the user is exposed to a risk of suffering a skin burn by touching the lamp that is hot after being lit. To prevent this, various measures have been proposed.
For example, projectors are known in which a door for lamp replacement is kept locked until the lamp has been cooled down, or a protective cover is provided around a lamp. A projector is also known that employs a turret-type lamp holder that can hold a plurality of lamps so that the lamp that is actually lit will be switched among them so as to prolong the substantial life of the lamp and thereby delay lamp replacement.
Locking a door until a lamp has been cooled down offers a high degree of safety, but, quite inconveniently, requires that the user wait for a while for the lamp to cool down before starting replacement with a new lamp he has prepared. Providing a protective cover around a lamp cannot be said to be the safest measure against a skin burn because heat is likely to conduct from the lamp to the cover, making the cover itself hot.
Employing a turret-type lamp holder so that the lamp that is actually lit will be switched among a plurality of lamps so as to prolong the life of the lamp helps lower the frequency of lamp replacement and thereby indirectly reduce the risk of a skin burn. However, in actual lamp replacement, there is as great a risk of a skin burn as where no measure has been taken, and thus some additional measure is required.
If the surface of the glass bulb of a lamp is stained with an inflammable greasy or similar substance, the lamp may burst when the lamp becomes hot by being lit. If the user directly touches a lamp, the glass bulb of the lamp is stained with seburn, which increases the risk of lamp bursting. Using a lamp unit having a lamp and a reflector integrated into a single unit somewhat reduces the risk, but there still remains a certain risk. In addition, it is uneconomical to replace the still usable reflector together with the lamp. The reflector is produced with high accuracy and thus at high cost to secure a satisfactory light-condensing ability, and therefore replacement of the reflector requires high cost.
Some lamps may burst if lit for a period longer than the life set therefor as a result of their glass bulb deteriorating as the lamps are kept lit. To prevent such lamp bursting and maintain safe display of images, it is necessary to manage the light-emission time of a lamp strictly.
To manage the light-emission time of a lamp, various methods have been proposed. A simple method is adding up the light-emission time of a lamp so that the lamp will cease to be lit when the added-up time has reached a predetermined period. There is a projector which displays the added-up light-emission time of a lamp. A projector is also known in which a label that changes the color thereof by reacting with ultraviolet rays is affixed in front of a lamp so that the user can visually check the light-emission time of the lamp.
However, according to the projector adding up the light-emission time, the light-emission time obtained is stored only on the part of the projector proper, and, every time a new lamp is fitted, the light-emission time stored until that time is erased and the light-emission time of the new lamp starts being measured. Thus, every time lamp replacement takes place, the data on the light-emission time of the older lamp is lost. Accordingly, if a lamp that has ever been lit for a while is fitted as a new lamp, the lamp is recognized as a lamp that has never been lit before. Thus, there is a risk that the lamp will be lit for a period far longer than the life thereof until the lamp eventually bursts.
Moreover, even though the lamp ceases to be lit when the light-emission time has reached a predetermined period, it is not possible to set the predetermined period differently for lamps having different ratings and thus different lives; that is, the predetermined period has to be a fixed value. Accordingly, with lamps having lives shorter than the fixed predetermined period, it is not possible to secure sufficient safety; by contrast, with lamps having lives longer than the fixed predetermined period, they cease to be lit with their lives partially left unused and thus quite uneconomically.
According to the projector employing the lamp provided with the color-variable label, the remaining life of the lamp is recorded on the part of the lamp itself. However, there is a possibility that, even while the lamp is not being lit, the label will change the color thereof by reacting with the light emitted from another lamp, and therefore a special measure is required for reliable recording of the remaining life. For example, in a construction that allows storage of a spare lamp inside the projector, light shielding is essential to prevent the light emitted from the lamp being lit from reaching the spare lamp.
In addition, to secure safety, the user is obliged to check visually the color of the label, and this can be a burden to the user. Usually, a member for modulating light is arranged in front of the lamp, and therefore it is not easy to conduct visual checking of the label directly. In particular, in a projector as is used as a television monitor in which leakage of light is undesirable, the lamp is housed inside a chassis, and thus cannot be observed from the outside. Accordingly, to check the remaining life of the lamp, quite inconveniently, the user needs to remove the lamp, which requires complicated handling.
Even a lamp that is unlikely to burst may become unable to be lit suddenly at the end of the life thereof. If the lamp being used becomes unable to be lit when no spare lamp is in stock, it is impossible to display images until a new lamp is procured.
To avoid this inconvenience, some projectors are furnished with a spare lamp in addition to a lamp that is actually lit so that the spare lamp will be lit when the lamp being lit becomes unable or unfit to be lit. For example, according to the abovementioned projector provided with the turret-type lamp holder, a lamp is lit in a predetermined position, and, when the current flowing through the lamp being lit drops below a predetermined value, the lamp holder is rotated so that a spare lamp will be moved to the predetermined position so as to be lit.
Some other projectors are so designed that, when the lamp being lit becomes unable to be lit, an indication will be displayed to request replacement of the lamp. For example, there is a projector provided with a sensor for detecting the amount of light emitted from the lamp so that, when the detected amount of emitted light drops below a predetermined value, an indication will be displayed on the screen to indicate that it is time to replace the lamp.
However, in conventional projectors, whether by switching the lamp being lit to a spare lamp automatically or by displaying an indication requesting replacement of the lamp, the necessary judgment is made indirectly by monitoring the current or the amount of emitted light, and thus it is impossible to manage the light-emission time strictly.
Moreover, in conventional projectors, the checking of whether a lamp is able or fit to be lit or not is performed only with the lamp that is currently being lit, and thus not with the spare lamp. Accordingly, there is a possibility that the spare lamp will be lit even if the spare lamp is not in a state fit to be lit; or there is a possibility that, when the lamp being lit becomes unfit to be lit, there will be no spare lamp fitted that is in a state fit to be lit, and thus it is impossible to display images.
To allow comfortable image viewing with minimum electric power consumption, it is preferable that a projector be so designed that the brightness of the image projected thereby is variable according to the ambient brightness. This is achieved in a projector proposed in Japanese Laid-Open Patent Application No. H9-96786. This projector is provided with a plurality of lamps as a light source for image projection so that the brightness of the projected image can be varied by varying the number of lamps lit simultaneously.
However, this method requires an ample space in which to arrange a plurality of lamps, and also requires an optical system for mixing the light from those lamps, making the projector as a whole unduly large. Moreover, the brightness of the projected image can be varied only stepwise, and thus, where fine adjustment of the brightness is desired, a large number of lamps need to be provided, making the projector even larger. In addition, to obtain uniform brightness over the entire image irrespective of the brightness thereof, it is necessary to keep the mixed light uniform irrespective of whether the individual lamps are lit or not. This requires an ingenious arrangement of the lamps or a special optical system, and thus complicates the construction of the projector.
Some kinds of lamp, such as a metal-halide lamp, allow their output, i.e. the amount of light they emit, to be varied according to the voltage applied thereto. By using such a lamp as a light source for image projection, it is possible to allow, with a single lamp, the brightness of the image to be adjusted easily and continuously simply by varying the voltage applied to the lamp. However, switching the voltage applied to the lamp with excessive frequency or applying a high voltage to the lamp for a long period shortens the life of the lamp, and in addition leads to uneconomical electric power consumption.
Moreover, in a lamp that offers a variable output, the color temperature of the light varies according to the output of the lamp. Accordingly, simply varying the output of the lamp causes the white balance of the displayed image to vary according to the brightness of the image, and thus leads to another disadvantage that images cannot be displayed with well-balanced hues at all times.
To change the state of an arc discharge lamp, as exemplified by a metal-halide lamp, from an unlit state to a lit state, the gas filling the lamp needs to be ionized. To achieve this, a projector applies a predetermined ignition voltage to the lamp for about one second. The lamp thus lit generates heat and becomes hot, and then, when extinguished, cools down gradually to room temperature. Subsequently, to display an image, the projector applies the ignition voltage to the lamp again to light the lamp.
However, in an arc discharge lamp, the ease of ionization of the gas varies with temperature, and therefore the ignition voltage required to light the lamp differs in low and high temperatures. For example, lighting a typical metal-halide lamp requires application of a voltage of 5 to 20 kV at low temperatures, and requires application of a voltage as high as 20 to 45 kV at high temperatures.
For this reason, while an arc discharge lamp is hot, as immediately after completion of image display, i.e. immediately after extinction of the lamp, quite inconveniently, it is impossible to light the lamp again to restart image display. For example, with a projector designed as a television monitor, if the user erroneously touches a switch on the remote control device of the television set and thereby finishes image display, image display cannot be restarted for a while, and thus the user is left unable to watch television meanwhile.
To avoid this inconvenience, some proposals have been made. For example, a projector is known that is provided with two metal-halide lamps so that, immediately after extinction of one lamp, the other lamp will be lit so as to achieve quick restarting of image display. There is also a projector having a delay function that prevents extinction of the lamp for a predetermined period even if the user operates for extinction of the lamp. A projector is also known that is provided with a metal-halide lamp and in addition an auxiliary lamp such as a halogen lamp so that, when image display is restarted immediately after extinction of the metal-halide lamp, the auxiliary lamp will be lit for a predetermined period.
These projectors allow image display to be restarted immediately after extinction of the lamp, and thus do not impose the inconvenience of waiting on the user.
However, even if two lamps are provided so that, immediately after extinction of one, the other will be lit, unless the two lamps are kept ready to be lit at any time, or in other words if either of them is unable to be lit, quick restarting of image display is impossible. Even if extinction of the lamp is delayed, it is invariably impossible to light the lamp again immediately after extinction thereof that takes place a predetermined delay period after. Even if an auxiliary lamp that can be lit quickly is provided, such an auxiliary lamp does not emit a satisfactory amount of light, and thus it is impossible to display images with satisfactory brightness for a predetermined period after restarting of image display.
Some types of lamp can be lit without application of an ignition voltage thereto. With such lamps, a voltage that is required to keep them in a lit state is applied thereto from the beginning. However, every such lamp has a specific light-emission temperature; specifically, the lamp starts emitting light only when the temperature of the lamp has reached the light-emission temperature after application of a voltage thereto. Accordingly, the lamp takes a longer time to start emitting light after application of the voltage thereto. In particular, when the temperature of the atmosphere is low, the lamp takes a longer time to reach the light-emission temperature and thus to start emitting light, remarkably delaying the starting of image display.
To prevent a lamp from becoming too hot while being lit, a projector is usually provided with a fan for air-cooling the lamp. Some projectors keep the fan rotating even after extinction of the lamp so as to promote cooling of the lamp and thereby shorten the time that the lamp takes to become able to be lit again. However, air-cooling promotes cooling of the lamp only in an indirect way, and therefore cannot satisfactorily shorten the time that the lamp takes to become cool enough to be lit again. Some lamps are structurally unfit for air-cooling, and therefore, in a projector employing such a lamp, it is impossible to quicken re-lighting of the lamp by fan-driven ventilation.
Moreover, a lamp should ideally be lit at the optimum temperature specific to the lamp. A lamp emits the maximum amount of light (i.e. offers the maximum brightness) at the optimum temperature, provided that the voltage applied thereto is fixed. The greater the deviation from the optimum temperature, the greater the negative deviation from the maximum brightness, and thus the lower the efficiency of light emission. However, to date, no consideration has been given to the optimum temperature in controlling the cooling of the lamp being lit even in a projector provided with a fan.
Broadly speaking, an object of the present invention is to provide a projector that achieves high-quality image display while offering excellent safety and user-friendliness. More specifically, principal objects of the present invention are as follows:
A first object is to provide a projector that makes the best use of a high-performance lamp.
A second object is to provide a projector that allows replacement of a lamp thereof without requiring any touch on the lamp.
A third object is to provide a projector and a light source that allow easy adjustment of the position of the light source.
A fourth object is to provide a projector and a light source that allow easy adjustment of the hues of the projected image.
To achieve the above objects individually or in combination, the present invention has the following aspects:
According to one aspect of the present invention, a projector is provided with: a light source; an image display device for performing spatial modulation on illumination light emitted from the light source on the basis of an image signal so as to form an optical image; and a projection optical system for projecting the optical image on a projection screen. Here, the light source is interchangeable with a light source of a different type.
According to another aspect of the present invention, a holding mechanism for holding a light source in a projector is provided with: a holding member for holding the light source; and an adjustment mechanism for adjusting the position of the light source by moving the holding member.
According to still another aspect of the present invention, a light source for use in an image projection apparatus is provided with: a light-emitting portion; a held portion that is held by the image projection apparatus when the light source is fitted in a predetermined position in the image projection apparatus; and data holding means for holding position-related data so as to allow the center of the light-emitting portion to be located at a previously specified position when the light source is fitted in the predetermined position.
According to still another aspect of the present invention, a projection-type image display apparatus is provided with: a lamp output varying device for varying the intensity of the light output from a lamp; a modulation device for performing modulation on the light output from the lamp in accordance with the color components of an image; and a controller for varying how the modulation device performs modulation in accordance with the intensity of the light output from the lamp so as to keep the white balance of the displayed image substantially constant irrespective of the intensity of the light output from the lamp.
According to still another aspect of the present invention, a projector is provided with: a light source; a reflector arranged around the light source; an image display device for performing spatial modulation on illumination light emitted from the light source on the basis of an image signal so as to form an optical image; and a projection optical system for projecting the optical image on a projection screen. Here, the light source is interchangeable with a light source of a different type. In addition, the projector is further provided with: an input section for inputting data in accordance with what type of light source is currently fitted; and a controller for performing a predetermined operation on the basis of the input data.
According to still another aspect of the present invention, a projector for projecting an image by using light from a light source is provided with: a holding member for holding the light source; and input means for inputting data in accordance with what type of light source is currently fitted.